My above-mentioned U.S. patent, which is based upon a French application which matured into French Pat. No. 2,452,587, discloses a support-arm assembly for a rockdrill especially suitable for use in subterranean operation, e.g. for drilling into the face of a mine gallery or tunnel as to advance the gallery or tunnel. Obviously, such systems are usable wherever a multiplicity of holes must be bored in rock or like structures, e.g. for the placement of explosives or simply to weaken the wall.
That assembly comprised a rail carrying a drilling head and means for displacing the head on the rail to drive the drill bit into the subterranean structure.
Since orientation of the rail in practically any direction is essential for versatility of the apparatus, that system comprised a base pivot or support which could rotate about a substantially vertical axis, a first hydraulic operator adapted to rotate the support or post about this axis, an arm articulated on this support for swinging movement about a substantially horizontal axis, a second hydraulic operator for swinging the arm, a support member on the arm rotatable about the longitudinal axis generally parallel to the arm, a third hydraulic operator for this latter means, and a cradle carrying the rail, pivotally mounted on the latter member, and a fourth hydraulic operator for tilting this cradle and hence the rail relative to the arm. Means was provided to control the respective operators so that the rail remains essentially parallel to itself for movement of the drill head into the various drilling positions.
In addition to the four movements described, which were effected by rotary hydraulic motors or hydraulic piston and cylinder arrangements forming the hydraulic operators, at least a fifth movement was provided by making the arm telescopically extensible by a fifth hydraulic operator such as a hydraulic piston and cylinder arrangement. This latter movement, however, does not have any effect upon the orientation of the rail although it is used to position it with respect to the subterranean structure which is to be drilled.
While this system was highly effective for most purposes, problems were encountered when, for example, it was desired to drill holes which converged or diverged, i.e. were not strictly parallel. In this case, automatic position compensation from hole to hole was not available and the holes had to be manually controlled which led to inaccurate drilling and inconveniences.
The earlier systems, moreover, which were provided with hydraulic correction only to a limited degree, were sometimes lacking in precision and thus did not provide suitable performance in many cases.
A third disadvantage was that the sensor of the rotary movement, i.e. the rotation of the cradle-carrying support member about the longitudinal axis of the arm, required rotary linear-output sensors which were rare and not always available.
Finally, it was not possible to provide fully automatic control of the drilling operation in accordance with, for example, a firing plan whereby a predetermined pattern of holes could be drilled in predetermined relationship and at the same time provide full manual control and positioning. It was especially difficult with the earlier system to manually position the rail at a desired location for initiating a sequence of automatic operations.